Process for determining acid or acidvapor formation characteristics of a substance



2,752,227 PROCESS FOR DETERMINING ACID OR ACID-VAPOR FORMATION E C N A T S B U m E Iv.

W m l mm F ma w mu F A H C June 26, 1956 INVENTOR W@LTUQF\NULAND 20 BY I W ATTORNEY PROCESS FOR DETERIVLHIING ACID OR ACID- VAPQR FORMATION CHARACTERISTICS OF A SUBSTANCE This invention relates to a method for accurately determining the temperature at which a substance, either liquid or solid, can be expected to liberate vapors of a corrosive or acid nature, either through oxidation or cracking or from the inherent nature of the material. In its broader aspects the process and apparatus of the present invention also may be used to determine the pH of vapors liberated from a substance under the influence of heat. More particularly, this invention is adapted for determining the acid or acid-vapor formation characteristics of a substance such as oils, greases and gases.

The stability of oils, and in particular lubricating oils, has been a vital problem for many years. First attempts to evaluate stability led to the development of a number of oxidation tests, such as the Indiana test and the Sligh test.

No oxidation test has ever proven to be adequate to evaluate all problems related to oil stabiltiy. These tests give no specific or direct information on the corrosive properties of the products of oil breakdown. It has been reasoned by those skilled in the petroleum art that vapors are probably liberated by a lubricating oil under conditions of elevated temperature and service, and that these vapors have a deleterious efi'ect on bearing metals and other metal parts.

Reactions in internal combustion engines are varied, complex and uncertain. Lubricating oil temperatures range from 220 F. in the oil sump on a warm day to 300 F. in the bearings and 400 to 500 F. at the ring belt. Oil is whipped around as a mist in the crank case and in this manner adsorbs considerable quantities of air. This adsorbed air serves to increase the rate of oil breakdown by at least three times when the oil is subjected to heat and pressure in the bearings and at the ring belt.

Lubricating oils, being hydrocarbons, are, under the conditions enumerated above, subject to oxidation. However, the breakdown process is necessarily very complex, and the order of events and the intermediate reactions produced depend on such factors as the structure of the original oil molecule, the temperature, pressure, presence of air, carbon monoxide, carbon dioxide, metallic catalyst and others. Such a combination of factors introduces a considerable element of uncertainty into any speculation about the nature of intermediate products.

The step-by-step oxidation might be illustrated by the progressive breakdown of a sample hydrocarbon .such as methane:

Methane methyl alcohol aldehyde-a crncrraort-sucno For-mic acid carbonic acid HCHO2 H2COs The heat genertates fiatent further reactions. This may mean partial cracking if the reaction is going on in larger molecules and the formation of methane, ethane, and other like hydrocarbons which are held in solution to more or less limited extent in the lubricating oil. The step-by-step oxidation will then proceed about as previously indicated for methane.

Ventillation of the crank case to remove the volatile acids is of no material advantage, because the damage appears to be done when the acids form, which is con siderably before they can be freed from the oil. The corrosive efiect of degraded lubricating oils on the metal parts of internal combustion engines and othermetal surfaces coming in contact with such oils is of considerable concern to automotive engineers and others concerned with this problem.

A new lubricating oil is composed of much larger molecules than indicated by methane, and upon initial oxidation, the higher aldehydes and acids, which may be said to be less harmful, form first. If progressive degeneration of the oil occurs, the lower, more corrosive acids make their appearance.

It is, therefore, a principal object of the present invention to provide a method and apparatus for determining the temperature at which a substance may be expected to either oxidize or break down under the influence of heat to yield acid vapors.

It is a further object to provide a means for giving specific and direct information as to the corrosive properties of the products of oil breakdown.

A still furhter object is to provide a method and apparatus which may be used in connection with any substance, whether liquids, semi-solids or solids, wherein the hydrogen ion concentration of the vapors liberated from the substance under the influence of heat may be ascertained.

The invention will be better understood by reference to the accompanying drawing showing a detailed illustration of the improved apparatus used in accordance with the present invention and in connection with which the invention will be described.

While, as previously mentioned, the invention may be used to determine the acid or alkaline vapor characteristics of any substance which is either oxidized under the influenceof heat to yield low boiling acids, or which con tains acids or bases initially, the invention will be de scribed in connection with the testing of a sample of lubricating oil to ascertain the acid properties of the products of oil breakdown.

The extent of oil breakdown can be determined by measuring the temperature at which volatile acids form. This may be readily accomplished by passing the vapors from the oil through a sensitive indicator as the oil is slowly heated and noting the temperature of the oil at which the indicator changes. Accurate and consistent results are possible when proceeding in the manner to be hereinafter described. The temperature at which acid vapors are first liberated is defined according to the present invention as the acid vapor temperature of the oil or substance being tested.

The acid vapor temperature of new lubricating oils ranges from 250 to 330 F. depending on the oil and the additives in the oil. If the oil is oxidized either by laboratory methods or on the road, acid vapor temperature gradually drops to a low of under F. The oil in this latter condition has long since passed its useful life.

It should be emphasized that the acid vapor temperature need not indicate the presence of free acids in the oil. It is, however, an indication of the temperature at which volatile acids form, and when this temperature drops to a rather definite point, it is an indication of incipient corrosion. For example, a lubricating oil must be considered as having approached the end of its useful life wherritsacid vapor temperature drops to 215 F.

According to the present invention, in order to determine the temperature at which volatile acids form and the temperature at which incipient corrosion ofmetalsurfaces in contact with such an oil may be. expected, asample of theoil to be tested isplacedin' a-suitable container such as the test tube 10, shown inFigureLwhich is-provided with a three holed stopper 11. A thermometer 14 is inserted into the container. through'stopper 11 so that it extends wellinto the sample 12 but without touching the walls of the-container 1i). The container It may be immersed into a second container 16-containing a suit able oil bath 18 or other heat'transfer medium. A-Bunsen burner 2G or other source ofheat is. placed. beneath container 18 and thesource: of: heat andcontainer 18 are protected from air currents-by'means of thesleeve device 22.

Air, oxygen or any other suitable gasv or. vapor, either singly or in desired proportions and hereinafter designated as air is conducted through the: air washing, drying and cleaning containers 24 -and 26. The. containers 24 and 25 may be filled with silicagelfor drying the air and sodium calcium hydrate for.- removal ofcarbon dioxide and other acid forming substances which may be in the air and which may aifcct the indicator. The pretreatment of the air is'not'for purposes of getting pure air for the reaction in the sample tube; but rather to-prevent foreign substances, particularly of anacid nature, from reacting with the indicator to be hereinafter referred to. The air moves from container 26 through. the air inlet tube 23 which extends nearly to the. bottom of the container 1t} holding sample 12 being tested;

The pre-washed and dried air is caused to bubble vigorously through a measured sample of the oil 12 being tested. While heat from burner 20 raises the temperature of sample 12 at a controlled rate, the bubbled air along with vapors from sample 12 are conducted from container 10 through tube 30 into the container 32 which contains a measured quantity of a sensitive indicator. To aid in detecting the'color' change of the-indicator, a small indirect light source may be used to illuminate it.

Tube 36 connects the stoppered container 321 to a suitable vacuum pump 38 which is used to draw the air through the system at a controlled rate. A- manometer may be inserted at some'convenient point in. the" train in order to maintain constant vacuum on the-systemduring the period of testing; While'a vacuum pump-has been described in connection with the'apparatus, it is. possible to use a pressure pump at the other end of the system invader to force the air through the train.

The rate of heating of the sample 12 isvery important, and it has been discovered that in-order'toobtain consistently accurate results the samplesshould be'heated approximately 10 F. per minute. However, good results have been obtained when heat was applied at not less than 1 F. per minute nor more than 60 F; per minute. The temperature of the sample, as measured by the. thermometer 14 inserted therein, at' which the-indicator 34 indicates'acidity is defined asthe acid-vapor temperatureof the sample.

in connection with the testing of substances other than lubricating oiis such as semi-solidor solidi'substa'nces; these may be placed in the container 10inv a partially crushed condition if desired andalso, dependingupon the nature of the substance, mixed with a suitable liquid of known properties. It is also. desirable whenworking with certain materials to pie-heat the air prior to introducing. it into the sample in the container 10.

While the indicator 34-may beany ofthe known acid or alkaline indicators-such as phenolphthalein; methyl red, and solid indicators; such'as litmus, it has been discovered that much more accurate results are obtainable-when an extremely sensitive indicator is used, such as a slightly alkaline alcoholic solution of methylene blue, which I have developed, and this indicator. ispreferred' when by- 4. drocarbons such as lubricating oils are being tested to determine their acid vapor temperature.

The methylene blue indicator, according to the present invention, is prepared as follows: To one liter of isopropyl alcohol, five to seven milliliters of a saturated solution of methylene blue in isopropyl alcohol is added along with approximately one milliliter of a saturated solution of potassium hydroxide in isopropyl alcohol. This mixture is allowed to stand for a period of approximately 24 hours, and after this period of standing should be of a red color. if, instead of red, the solution is found to be purple, a few additional drops of potassium hydroxide in isopropyl alcohol. should beadded. The indicator may then be checked for sensitivity by adding one drop of 0.1 N benzoie acid solution in isopropyl alcohol to ten milliliters of the indicator. If the indicator is of the proper degree of sensitivity, this should turn the solution definitely blue.

The total heating time for the sample being tested is also of importance in reaching accurate results, and it has been found that thetotal heating time of the sample should not be over ten minutes. As pointed out, the acid vapor temperature of oils ranges from approximately 330 F. for new oils to-as low as F. for severely deteriorated. oils. The danger zone, that is, the point at which. the oils become corrosive, occurs when the acid vapor temperature drops to 200 to 215 F.

When proceeding according to the present invention, it has been discovered to be essential to have the washing and drying containers 24 and 26 for the air which is to be bubbled through the samples. It has also been discovered that the ebullition of the air through the sample must be vigorous and that the air along with occluded vapors from the sample must also be brought into intimate and vigorous contact with a measured quantity of the indicator in the container 32.

The following examples illustrate the manner of proceeding according to the present invention. These examples are illustrative only and the intention is not intended to be limitedby the examples disclosed but only by the scope of the appended claims.

Example I A measured sample of lubricating oil is placed in the container 10. Vacuum pump 38 is activated and adjusted to draw a stream of pre-washed an dried. air. through tube 28 at a rate so that the air will bubble vigorously through the sample. in the container 10. The air and-vapor from the sample being tested are conducted to a measured sample of methylene blue indicator in the container32 so as to have vigorous and intimate contact with the indicator. Simultaneously with the movement of air through the system the sample. of. oil is heated approximately 10 F. per minute. As the temperature of' the sample of oil rises, as indicated by the thermometer 14, a continued observationof themethylene blue indicator is maintained, and the temperature of the sample at which the indicator first shows acidity indicates the temperature at which acid vaporsmay be expected to form from the oil in use.

Example II The procedure for testing greases, highly viscous substances, pastes and semi-solids is as follows:

A measured sample of the substance is thoroughly mixed with a suitable solvent or thinner of known characteristics, and preferably one that. is reasonably stable, and in such proportions as to render the mixture of the consistency of thin molasses. A measured sample of the mixture is placed in the container 10. The procedure is then continued as for Example I.

In connection with the above example, greases thinned with fresh lubricating oil have shown acid vapor temperatures as low as F. Used greases have shown much lower temperatures.

In' the case of lubricating oils' and greases the lowering ofacid vapor temperature is a-measure of the extent of degeneration and an indication of incipient corrosion. These facts have been established by abundant experiments. In the case of paints, varnishes, molasses, foods, etc., the acid vapor temperature or the evolution of volatile acids could very well be a measure of their stability, rate of degeneration and other properties which would be valuable to determine storage characteristics.

Example 111 Procedure for testing solid material.Whenever practical the solid should first be crushed or pulverized by suitable means. A measured sample of the dry solid material is placed in container 10. A filtering device such as a wad of surgical cotton is placed in container a short distance below stopper 11 to prevent dust from the sample being carried over into the indicator 34. Under extremely difiicult conditions an additional con tainer which serves as a trap to catch any dust which may pass through the filtering medium may be inserted in line 30 between container 10 and container 32. The procedure is then continued as in Example 1.

Example IV A measured sample of the dry crushed or pulverized material or of wet crushed material, is suspended in a quantity of distilled Water, or in a quantity of high boiling point liquid of known properties, and the suspension placed in container 10. The procedure is then continued as in Example I.

In connection with running tests to determine the acid vapor temperature of solids, an extended investigation on soil corrosion has just been completed under my direction. In evaluating the soil to determine the constituents responsible for corrosion, volatile organic acids were suspected. The procedure of Example III and Example IV were applied. For the several soils tested acid vapor temperatures ranging from 170 F. to 215 F. were discovered which verified these suspicions.

Soils are rarely subjected to these temperatures. However, volatile organic acids will form more slowly under normal soil temperatures. These become serious corrosion hazards which may be especially severe where pipe lines are buried at shallow depths. An extreme example of this reaction may be illustrated in the case of a copper line buried about one foot underground in rich soil. The line completely disintegrated in about 14 months.

Example V Effect of volatile vapors on metal.-The procedure is the same as for Example I, except that a sample of the metal to be tested is substituted for the indicator 34.

Example VI A cleaned strip of metal is placed in container 32 in place of the indicator, and the metal is partially submerged in distilled water. The pre-washed and dried air is vigorously bubbled through sample of substance in container 19, then brought into intimate and vigorous contact with the distilled water and metal in container 32. Simultaneously the sample 12 is heated at a specified temperature for a specified time. The metal is then removed from the distilled water, and the distilled water is checked for metal traces in solution or suspension by any of the known and published micro-chemical or colorimetric methods suitable for the particular metal.

Example VII A cleaned strip of metal is placed in the dry container 32. A second and similar container with a quantity of distilled water is inserted in line 36 and between container 32 and vacuum pump 38. Prewashed and dried air is bubbled vigorously through the sample of substance in container 10; the gas and vapors from sample 12 are specified temperature for a specified time.

strip, and thence through the second container where said vapors are bubbled vigorously through the distilled water. Simultaneously sample 12 is heated at a constant The distilled water is then checked for metal as in Example V.

The corrosive etfect on metals of vapors from oils whose vapor temperature had been lowered by laboratory oxidation and from oils used in engines has been repeatedly demonstrated as per Examples V, VI and VII. Metal traces have been detected in the distilled water after as short a heating period as 15 minutes of an oil whose acid vapor temperature had dropped to 215 F. and which was heated during-this test at 215.

Positive corrosion results have also been obtained with solids such as the soils of Example HI.

Example VIII Procedure for testing gases.A substance which'is a gas or vapor at normal temperatures is drawn into the dry container 10 through a T in the inlet tube 28 at a specified rate and manner. With suitable adjusting valves, air may or may not, as the conditions require, be drawn in desired proportions through containers 24 and 26 and become mixed with the gas or vapor in tube 28 and container 10. The air and gas or vapor mixture from container 10 are conducted to a measured sample of methylene blue indicator in container 32 so as to have vigorous and intimate contact with the indicator. Simultaneously with the movement of air and sample through the system the sample is heated approximately 10 F. per minute. As the temperature of the sample rises as indicated by thermometer 14, a continued observation of the methylene blue indicator is maintained, and the temperature of the sample at which the indicator first shows acidity indicates the temperature at which acid vapors form and is a measure of the stability of the gas.

The feasibility of this procedure as applied to gases and vapors has been demonstrated in the case of gasoline vapors. The general procedure has been used except that the indicator has been replaced with a strip of metallic copper to determine the corrosive effect of the vapors directly.

I claim:

1. A process for determining the acid vapor formation characteristics of a substance selected from the group consisting of lubricating oils and greases and mixtures of the two, said substance having an acid vapor temperature not above about E, which comprises the steps of applying heat at a continuously increasing temperature at a controlled rate to the sample to be tested and simultaneously with said application of heat passing a stream of pro-washed and dried gas vigorously through said sample, conducting the gas and vapors from said sample to a measured quantity of a volatile, acid-sensitive indicator and measuring the temperature of the sample at the precise time that said volatile, acid-sensitive indicator indicates the presence of acidic vapors in the gas and vapor prod ucts bubbling through said indicator, whereby from the temperature of said sample at which said indicator shows the first indication of acidity the acid vapor temperature of the sample may be ascertained.

2. A process as claimed in claim 1 wherein the rate of heating of said sample is 10 F. per minute.

3. A process as claimed in claim 1 wherein the rate of heating of said sample is within the range of 1 F. to 60 F. per minute.

4. A process as claimed in claim 1 wherein the bubbled gas and vapors from said sample are caused to have intimate and vigorous contact with said acid indicating medium.

5. A process as claimed in claim 1 wherein the gaseous substance comprises oxygen and mixtures thereof.

6. Aprocess as claimed in claim 1 wherein the gaseous 7 substance is pre-heated to accelerate the breakdown of the test sample.

References Cited in the file of this patent OTHER REFERENCES Gas Chemists Handbook, pages 267, and 268, March 1, 1922, 2nd ed., publication by American Gas Association, N. Y. C.

Grettie: Ind. and Eng. Chem, Anal. Ed, vol. 3, pages 171-173, April 15, 1931.

Royce: Ind. and Eng. Chem, Anal. Ed, v01. 5, pages 244-247, July 15, 1933.

Fenske at 211.: Ind. and Eng. Chem, Anal. Ed, vol. 13, pages 51-60, Jan. 15, 1941.

Fuchs et aL, Ind. and Eng. Chem, Anal. Ed, vol. 13, pages 306-312, May 15, 1941.

Lamb et al.: Ind. and Eng. Chem, Anal. Ed, v01. 13, pages 317-321, May 15, 1941.

Hersh et a1.: Petroleum Refiner," vol. 22, N0. 7, pages 197-205, July 1943.

Burk et al.: I. and E. Shem., Anal. Ed, v01. 17, No. 5, pages 302-309, May 1945.

Rescorla et al.: I. and E. Chem, Anal. Ed, vol. 9, No. 12, pages 574-576, Dec. 15, 1937.

Balsbaough et al.: I. and E. Chem, Anal. Ed, vol. 13, No. 7, pages 515-519, August 15, 1941.

Mme- 

1. A PROCESS FOR DETERMINING THE ACID VAPOR FORMATION CHARACTERISTICS OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF LUBRICATING OILS AND GREASES AND MIXTURES OF THE TWO, SAID SUBSTANCE HAVING AN ACID VAPOR TEMPERATURE NOT ABOVE ABOUT 160* F., WHICH COMPRISES THE STEPS OF APPLYING HEAT AT A CONTINUOUSLY INCREASING TEMPERATURE AT A CONTROLLED RATE TO THE SAMPLE TO BE TESTED AND SIMULTANEOUSLY WITH SAID APPLICATION OF HEAT PASSING A STREAM OF PRE-WASHED AND DRIED GAS VIGOROUSLY THROUGH SAID SAMPLE, CONDUCTING THE GAS AND VAPORS FROM SAID SAMPLE TO A MEASURED QUANTITY OF A VOLATILE, ACID-SENSITIVE INDICATOR AND MEASURING THE TEMPERATURE OF THE SAMPLE AT THE PRECISE TIME THAT SAID VOLATILE, ACID-SENSITIVE INDICATOR INDICATES THE PRESENCE OF ACIDIC VAPORS IN THE GAS AND VAPOR PRODUCTS BUBBLING THROUGH SAID INDICATOR, WHEREBY FROM THE TEMPERATURE OF SAID SAMPLE AT WHICH SAID INDICATOR SHOWS THE FIRST INDICATION OF ACIDITY THE ACID VAPOR TEMPERATURE OF THE SAMPLE MAY BE ASCERTAINED. 